Recovery of selenium



Patented Jan. 30, 1934 UNITED STATES PATENT QFFICE Aria, assignors to United Verde Copper Company, a corporation of Delaware No Drawing.

Application November 11, 1930 Serial No. 494,923

12 Claims.

This invention relates to metallurgy and has for an object the provision of an improved process for treating copper ores. More particularly, the invention contemplates the provision of an improved process for obtaining a copper product suitable for purification by electrolysis. The invention further contemplates the provision of a process for recovering selenium from metal products.

Copper ores frequently contain, in addition to iron and other gangue materials, impurities such as arsenic, antimony, selenium and telluriurn, some of which are eliminated during smelting operations and others of which are retained by 15 the blister copper and eliminated during the electrolytic operations. The impurities may be present in commercial amounts and in sufficiently large quantities to reduce the efficiency of the electrolytic operations.

It is customary for the independent producers to send their blister copper to custom refineries for treatment. When the blister copper contains harmful impurities, the producers may be penalized by the refiners, and, in some instances, notably in the case of selenium, even though the blister copper contains commercial amounts of the so-called impurities, no credit is given the producers.

It is desirable to so conduct metallurgical operations for the treatment of copper ores as to avoid the incorporation of impurities in the blister copper in order to improve the eiliciency of the electrolytic operations and/or to recover a valuable commercial product.

The present invention is based on our discovery that a relatively pure copper product may be obtained by subjecting blister copper or the product of a converting operation between the stages of white metal and blister copper, in the form of a molten bath, to the action of a slag containing one or more alkali metal compounds. We have found that such slags are particularly effective for recovering selenium. The treatment for the recovery of selenium is most effective when conducted in a reducing environment.

In carrying out the process of the invention, we prefer to employ a highly basic slag containing an amount of alkali metal oxide in excess of that which is satisfied by the acid forming constituents. Slags for use in the process of the invention may be formed in any desired manner. Alkali metal oxides, or other suitable compounds of alkali metals like sodium and potassium, may be applied to the surface of a molten copper bath, or, molten copper may be treated with an alkali metal such, for example, as metallic sodium in the presence of sufficient non-metallic oxides to form a slag with the resulting sodium oxide, sodium sulphide, and sodium selenide.

As a result of our discovery, we propose to 0 modify the usual copper smelting practice to include a step involving the treatment of blister copper, or the product of the converting operation immediately before it reaches the blister copper stage, in the form of a molten bath, with a slag containing one or more alkali metal compounds. The converting operation is continued until impurities such as iron and other gangue materials have been eliminated and white metal has been produced. Blowing of the white metal 7 may be continued until the blister copper stage has been reached, but it is preferably discontinued when the major portion of the sulphur has been eliminated. We have found that a white metal or blister copper product containing about two percent of sulphur may be treated effectively.

In treating a selenium-bearing copper sulphide ore for the recovery of selenium, the ore is first smelted in a blast or reverberatory furnace tr. Q produce a matte suitable for converting. The matte is placed in a converter and treated in the usual manner until white metal has been produced. The white metal is blown until a product containing about two percent sulphur is obtained. This product is then transferred from the converter to a suitable furnace such, for example, as a refining furnace and covered with a layer of slag containing an alkali metal compound, preferably, a soda slag. We have used, successfully, slags formed from trona, an impure sodium carbonate containing about five percent lime.

The slag covered bath is agitated and subjected to the action of a reducing agent. The reducing action and agitation may be accomplished by injecting oil, reducing gas, powdered coal or coke through tuyeres below the surface of the bath or by poling. Agitation may be continued until the sulphur and selenium are substantially completely eliminated from the copper of the bath. The purified copper may be cast into molds. The selenium will be found in the slag, probably in the form of an alkali metal selenide which may be placed in solution by leaching with water. The selenium may be recovered from the solution in 1 any suitable manner, as, for example, by passing air or sulphur dioxide through the solution to effect precipitation.

The slag may be treated for the recovery of selenium after treating a single batch of copper or an enriched product may be obtained by using the same slag for treating several batches.

We claim:--

1. The method of treating copper sulphide ore which comprises smelting the ore to produce matte, treating the matte to eliminate sulphur, and subjecting the resulting product in the form of a molten bath to the action of a slag containing one or more alkali metal compounds under reducing conditions.

2. The method of treating copper sulphide ore which comprises smelting the ore to produce matte, treating the matte to eliminate sulphur, and subjecting the resulting product in the form of a molten bath to the action of a slag containing one or more alkali metal oxides under reducing conditions.

3. The method of treating copper sulphide ore which comprises smelting the ore to produce matte, treating the matte to obtain a product containing about two-percent sulphur, and subjecting the resulting product in the form of a molten bath to the action of a slag containing one or more alkali metal compounds under reducing conditions.

4. The method of treating copper sulphide ore which comprises smelting the ore to produce matte, treating the matte to obtain a product containing about two-percent sulphur, and subjecting the resulting product in the form of a molten bath to the action of a soda slag under reducing conditions.

5. The method of treating copper sulphide ore which comprises smelting the ore to produce matte, subjecting the matte to a converting operation until a molten product containing about two-percent sulphur is obtained, and subjecting the resulting product to the action of a soda slag under reducing conditions.

6. The method of recovering selenium from copper sulphide ore which comprises smelting the ore to produce matte, subjecting the matte to a converting operation until a product containing a small percentage of sulphur is obtained, subjecting the resulting product in the form of a molten bath to the action of a slag containing one or more alkali metal compounds under reducing conditions, and treating the slag to recover selenium.

'7. The method of recovering selenium from copper sulphide ore which comprises smelting the ore to produce matte, subjecting the matte to a converting operation until a product containing a small percentage of sulphur is obtained, subjecting the resulting product in the from of a molten bath to the action of a soda slag under reducing conditions, and treating the slag to recover selenium.

8. The method of recovering selenium from copper sulphide ore which comprises treating the ore to form a molten bath of blister copper, subjecting the blister copper to the action of a slag containing one or more alkali metal compounds under reducing conditions, and treating the slag to recover selenium.

9. The method of recovering selenium from copper sulphide ore which comprises treating the ore to form a molten bath of blister copper, subjecting the blister copper to the action of a soda slag under reducing conditions, and treating the slag to recover selenium.

10. The method of recovering selenium from copper sulphide ore which comprises treating the ore to form a molten bath of blister copper and subjecting the molten blister copper to the action of an alkali metal in the presence of one or more slag forming compounds.

11. The method of treating selenium-bearing metal to remove the selenium therefrom which comprises subjecting the metal in the form of a molten bath to the action of a slag containing OLIVER C. RALSTON. LEONARD KLEIN.

subjecting the metal in the form of a ii 

